Migrate batch and block proving to miden-base

[Mirko-von-Leipzig]

Some block-producer types ought to live in miden-base.

Specifically:

• BlockNumber, which is currently a weak type alias in base. This should become a strong new-type instead.
• TransactionBatch which should become ProposedBatch so that the (eventual) batch proving kernel has a target
• Similarly ProposedBlock and block proving kernel
• BlockWitness is also a probably moving target
• BatchId should also move with the batch stuff

[bobbinth]

I'm thinking on the miden-base side, we'll have dedicated crates to handle batch and block construction/proving (similar to how we have miden-tx crate to encapsulate transaction execution/proving logic). These crates should be much simpler than miden-tx: they would probably need to expose just a single function each. For batch prover, this function would take ProposedBatch + maybe something like BatchWitness and return ProvenBatch. For blocks, it would work similarly: take ProposedBlock + BlockWitness and return just Block.

After this, next step would be to add add proving services to for batch and block provers (similar to how we have a miden-tx-prover service) which would allow us to use a pool of workers to build proofs. Then, the node would just make requests to these services for batch/block construction.